In new pickup trucks, the walls of the truck bed are usually painted with a color similar to that on the external side walls of the vehicle. When the trucks are new, the beds, which can be easily seen from outside the vehicle, appear essentially as attractive as the external finish on the vehicle. However, with use of the truck to haul materials, packages, and other articles, particularly those which are relatively heavy, the bottom and sides often become scratched and scraped to the extent that the metal of the bottom and side walls becomes exposed and, hence, often becomes rusted and discolored. This seriously detracts from the appearance of the truck bed and often renders it unsuitable for other than industrial or agricultural uses of the vehicle, such as for family errands or mere transportation. In order to prevent this damage to the internal walls of the truck bed from occurring, industry has developed and used a liner, which fits into the bed, resting on the bottom and against the forward end and side walls. This liner provides effective protection to the side walls, so that, when the truck is to be used for only transportation and similar purposes, or when it is to be sold, the liner can be removed and the original paint then exposed in substantially the same condition as it was when the truck was initially purchased. Further, the liner normally is made of plastic material which will withstand the abrasive effect of the materials or products hauled in the truck and can be cleaned more effectively than the original truck bed.
In the past, in order to secure the liner in place in the truck bed, the liner was provided with outwardly extending flanges at the upper edges of the two side walls, with the flanges extending outwardly over the upper edge of the two walls and in close proximity thereto. Holes were drilled through the flanges into the upper edges of the sides of the truck bed, and screws were inserted therein to secure the flanges and, hence, the liner in place in the bed. This type of structure, which was extensively used in the trade to secure the liner in place, had several disadvantages, including the drilling of holes in the upper edges of the new side walls of the bed, which exposed the bare metal in the side walls of the truck and, hence, permitted corrosion to take place, so that when the truck was to be sold, the upper edges of the side walls were disfigured, possibly decreasing the sale price of the used truck. Further, the truck liners being of a plastic material and the truck beds being of a metal material resulted in nonuniform expansion when they were subjected to heat and cold; hence, there was a tendency for the flanges and portions of the side walls of the liner to buckle as the bed and liner were exposed to the hot sunshine. This placed a strain on the liner and, in some instances, resulted in cracking of the flanges in and around the screws, eventually requiring replacement of the liner. Since the truck beds were of sheet metal, the exposed metal around the holes of the securing screws readily rusted and disintegrated, so that substantial damage was done to the upper edges of the sides of the bed, and sometimes resulted in the loosening of the screws and, hence, loosening of the liner in the bed.
Another type of liner securing means which has been used commercially consists of expansion anchoring bolts extending through the outwardly extending flanges into the stake pockets of the bed side walls. This type of securing means also has much the same disadvantages as the previously described screws in the flanges, particularly with respect to the nonuniform expansion of the bed liner in response to changes in temperature.